Sodium hypochlorite solutions are commonly used and highly effective as bleaches and sanitizers for cleaning a variety of surfaces. However, sodium hypochlorite solutions are extremely corrosive to many treated surfaces, in particular, metal surfaces become highly corroded. Hypochlorite solutions corrode surfaces as a result of its composition of sodium hypochlorite, sodium chloride and often sodium hydroxide, each having distinct mechanisms of corrosion. Sodium hypochlorite is a strong oxidant causing metal corrosion through a redox attack. Sodium chloride attacks and penetrates the passivation layer of metals, resulting in pitting of the surface. In addition, sodium hydroxide is corrosive to metals as a result of formation of metal hydroxide. Additional descriptions of the mechanisms of corrosion are disclosed in Corrosion Basics, National Association of Corrosion Engineers, 1984.
Electrolysis as a water treatment process can be used to produce hypochlorite cleaning solutions. It is well understood that electrolysis methods employ electricity entering a water source at a cathode and passes through the water, exiting through an anode. Hydrogen is collected at the cathode (negatively charged electrical current) and oxygen is collected at the anode (positively charged electrical current). The reaction of water in an electrolytic cell is a redox process, wherein an oxidation reaction occurs at the anode while a reduction reaction occurs at the cathode. Various types of conventional electrolysis cells and methods for electrolyzing water are known and disclosed, for example in U.S. Pat. Nos. 3,616,355, 4,062,754, 4,100,052, 4,761,208, 5,313,589, and 5,954,939. Such electrolysis cells are used for a variety of purposes. Depending upon the structure of an electrochemical cell and the input salt source, various effluents may be produced, including for example, hypochlorous acid, sodium hydroxide (caustic) and hypochlorite (sodium hypochlorite, commonly referred to as bleach).
The on-site production of chlorine-containing oxidant products such as sodium hypochlorite, hypochlorous acid, chlorine and/or Cl2 from aqueous sodium chloride solutions are desirable, as production from an electrolyzed water process prevents the need to transport diluted aqueous solutions of the corrosive products such as hypochlorite or difficult to transport corrosive and flammable gases such as chlorine gas. Such products produced from an electrolyzed water process may be referred to herein as “electrolyzed water products.” Alternatively, electrolysis cells may be used to generate alkaline sources, such as potassium hydroxide and potassium sulfate through electrolyzing sodium sulfate. See e.g., U.S. Pat. No. 6,375,824.
The effectiveness and convenience of utilizing electrolysis systems are frequently limited due to the failure of the electrodes and membranes of the cells caused by corrosion and/or hard water scaling. The longevity of the electrodes and membranes of the cells are significantly diminished when scaling and/or corrosion are observed in the cell. There remains a significant need to inhibit fouling of electrochemical cells in order to prolong the lifetime of an electrochemical system. There is also'great demand for high-economic-efficiency operation conditions for improved electrolysis systems.
It is an objective of the claimed invention to incorporate corrosion inhibitor compositions to improved electrolyzed water products in order to prevent all corrosive mechanisms of sodium hypochlorite solution on metal surfaces.
A further object of the claimed invention is an improved electrolyzed water product containing a corrosion inhibitor composition capable of preventing metal corrosion caused by sodium hypochlorite solutions without adversely impacting the stability of the hypochlorite solution.
A further object of the invention is to provide methods for improved hypochlorite generation using electrolysis in a variety of electrochemical cells, including portable electrochemical cells for onsite generation of smaller quantities of hypochlorite for a variety of cleaning applications.